External Validity

External validity refers to the degree to which the relations among variables observed in one sample of observations in one population will hold for other samples of observations within the same population or in other populations. External validity is often treated as synonymous with the generalizability of results. Whenever empirical research makes use of a sample to examine how two or more variables are related within a larger population or whenever one seeks to extend results drawn from one population to a new population, questions of external validity arise.

External validity is often contrasted with internal validity or the question of whether valid inferences can be reached regarding the existence and nature of a relationship between two variables. Efforts to increase internal validity often reduce a ...